free-space-fragmentation · shipping · also free space fragmentation

Free-space fragmentation

Free-space fragmentation is the division of a filesystem's available allocation space into separated contiguous runs.

Related Observatory article: Free-space fragmentation on hesela.com

The same number of free blocks can have different run sizes and locations. This constrains later allocation, but free space itself is not read in a scan of allocated file contents. Geriatrix targets both allocated-file and free-space layout.

Relations

related

filesystem-aging, dynamic-layout-score, ssd-preconditioning

Limitations

• An occupancy percentage is not a free-extent distribution.
• Logical free runs do not reveal the physical NAND layout behind an SSD's mapping layer.

Citations

1. Kadekodi, Nagarajan, Ganger and Gibson. Geriatrix: Aging what you see and what you don't see. USENIX ATC 2018, pp. 691-704, sections 4-6. (accessed 2026-10-14)
2. Conway et al. Filesystem Aging: It's more Usage than Fullness. HotStorage 2019, sections 3-4 and Figure 3. (accessed 2026-10-14)

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